This invention generally pertains to apparatus for grinding or comminuting and the like. More specifically, the invention relates to a liner assembly for the interior shell of a grinding mill.
Grinding mills are used for the purpose of reducing the size of lumps or other pieces of ore and the like. In the case of ore, the normal function of the grinding mill is to reduce the size of the ore to particles within a fine sieve range for flotation in which, through the use of suitable additives, the ore bearing particles are separated from the gangue. Grinding mills of this type may employ rods or balls to assist in the comminuting process as the mill is rotated. In addition to balls or rods which are generally made of alloy steels, pebbles or natural rock have also been used as grinding media. Such grinding mills typically are comprised of cylindrical shell arrangements rotated about their longitudinal axes, and wherein the shells are closed on the opposite ends thereof. Different diameters and lengths of shells have been utilized heretofore, and they normally vary in proportion to the capacity of the mill.
In modern, large automatic mills the ore may be self grinding. An example of this type of mill comprises a large cylindrical drum mounted on bearings for rotation about its longitudinal axis, and wherein the drum is driven by a motor through conventional reduction gearing. The axial ends of the drum may be open, and the material to be comminuted can be continuously fed into the mill at one end with the comminuted product continuously emerging from the other end.
In view of the basic character of the material being ground, the wear on the inside of the grinding mill has been a serious problem. Normally, grinding mills have been lined with cast or wrought abrasion resistant ferrous alloy liners several inches thick, or in some cases, with rubber or ceramic liners. These liners are segmented due to weight and size considerations. That is, the liner assemblies comprise a plurality of separate components which are usually retained tightly against the interior of the mill shell by mechanical fastening means. During service, the liners tend to be worn easily by the abrasive action of the grinding media and the ore being ground in the mill.
The cost of periodic replacement of liners represents a major item of expense in the operation of mills or plants which grind ore or other minerals. In addition, it is evident that maintaining an ore grinding mill in operation as continuously as possible and keeping downtime for maintenance or repair to a minimum has economic benefits. However, many ores, e.g. taconite, are extremely hard and highly abrasive, and in order to maintain continuous operation of the grinding mill, it is necessary to provide a liner for the drum which is highly abrasion resistant. The liner also should be tough enough to withstand the continuous impact of ore fragments.
Liner segments which are formed with wear insert sockets having a special shape are known in the art. These linear segments are retained within a cylindrical grinder shell by threaded fasteners having heads received in the sockets and shanks passing through both the segments and shell to receive nuts at the shell outer surface. In this type of liner segment, the sockets and heads are shaped to provide continuous flat contact areas of substantial size, regardless of variations in center distances of holes disposed axially along the shell. One difficulty with this type of liner segment is that the structural configuration involved is unnecessarily complex. Another difficulty resides in the fact that the wear inserts provided in the liner segment sockets do not extend over the entire length of the liner, but rather, are discontinuously spaced therealong. Similar problems exist with a type of insert in which the harder material is poured into a "pre-made" casting. Another problem with some types of liner segments is that an unnecessarily complex securing assembly is required to affix the liner to the shell.
The use of hardened wear inserts substantially increases the life of the liner assembly, and as a result, reduces the downtime encountered with previous liner assemblies. A hardened insert in a softer material also maintains a higher lifting surface rather than flattening over the entire surface, thus promoting greater agitation of the rod or ball charge. However, the changing of the known types of liner assemblies remains an arduous task and a substantial number of man-hours is required. This is due primarily to the manner of connecting the known liner segments to the shell. The problem is compounded by the substantial size and weight of each liner segment, and the damage incurred by the segments and connecting bolts from the continuous impact of ore fragments during the comminution process.
It would, therefore, be desirable to have an improved liner assembly for ore grinding mills which is easily replaceable. At the same time, such assembly should preserve the substantial benefit derived from the use of abrasion resistant wear inserts. It would, moreover, be desirable to have a liner assembly in which the wear insert is securely wedged in place in a holder segment. It would also be desirable to provide interlocking ribs and recesses in the holder segments, the wear inserts, and the wedging members for preventing lengthwise movement by either the wedging member or the wear insert with respect to the holder segment.
The subject invention overcomes the above noted difficulties and others, and is deemed to meet the foregoing desirable design parameters.